The invention relates to air-conditioning circuits, in particular for motor vehicles.
A conventional air-conditioning circuit essentially comprises a compressor, a condenser, a pressure-reducing valve and an evaporator traversed, in that order, by a refrigerant fluid. The latter is compressed in the gaseous phase by the compressor, converted into liquid phase in the condenser, reduced to low pressure by the pressure-reducing valve, converted into gaseous phase in the evaporator, and so on.
In a conventional air-conditioning circuit of a motor vehicle, the compressor is driven by the engine of the vehicle by way of a clutch mechanism, so that the rotational speed of the compressor is always proportional to that of the engine of the vehicle.
In order to avoid this drawback, it is also known to use an electric compressor, that is to say a compressor actuated by an electric motor through appropriate control means, so that the rotational speed of the compressor is independent of that of the engine of the vehicle.
In this case, the control means associated with the electric compressor usually comprise a regulation-electronics card suitable for driving the electric motor of the compressor under defined conditions.
However, such an electronics card is complex and expensive to produce, and may, moreover, be subject to malfunctions.
The object of the invention is especially to surmount the abovementioned drawbacks.
The invention aims, in particular, to procure a device for control of a compressor actuated by an electric motor which is of a particularly simple and robust design, and which does not require the use of an electronics card.
It also aims to procure such a control device which, in addition to its simplicity and its reliability, nevertheless guarantees safe operating conditions for the compressor.
According to the present invention there is provided device for control of a compressor actuated by an electric motor for an air-conditioning circuit, the device comprising an inverter suitable for applying a variable frequency to the electric motor under the control of a control circuit, so as to adjust the speed of the electric motor, wherein the control circuit comprises a potentiometer having end terminals linked respectively to an earth terminal and to a maximum-voltage terminal of the inverter, as well as a slider terminal linked to an intermediate terminal of the inverter by way of a control line, and wherein the control line is equipped with a first two-position switch in order to control a normal-operation mode under the control of the potentiometer and a degraded-operation mode.
The invention proposes a control device of the previously defined type, which comprises an inverter suitable for applying a variable frequency to the electric motor under the control of a control circuit, so as to adjust the speed of the electric motor. The control circuit comprises a potentiometer having end terminals linked respectively to an earth terminal and to a maximum-voltage terminal of the inverter, as well as a slider terminal linked to an intermediate terminal of the inverter by way of a control line. This control line is equipped with a first two-position switch in order to control a normal-operation mode under the control of the potentiometer and a degraded-operation mode.
Moreover, the control line is preferably linked to earth via a second switch in order to prevent operation of the electric motor under defined conditions.
Thus, the control device of the invention is particularly simple to produce since it essentially comprises a control circuit with a potentiometer and at least one controlled switch, this control circuit being associated with an inverter the output of which is linked to the electric motor of the compressor.
Such a device is particularly reliable and achieves operation under maximum safety conditions.
It avoids having recourse to a complex electronics card or to a microprocessor.
In the normal operating mode, the control line is linked to the potentiometer, actuation of which makes it possible to set the power-supply frequency of the electric motor.
The first switch is suitable for controlling a degraded-operation mode, in which the speed of the electric motor of the compressor can be brought to a low value under pre-defined conditions.
Moreover, the second switch, if it is present, makes it possible to prevent operation, that is to say to stop the electric motor of the compressor, under defined conditions. As will be seen further on, the moving of the first switch from the normal-operation mode to the degraded-operation mode is carried out automatically, and the same is true for the closing of the second switch which prevents the operation of the electric motor of the compressor.
Put another way, the control of the first switch and of the second switch takes place without any intervention by the user.
In one preferred embodiment of the invention, the first switch possesses a first position in which the control line is linked to the slider terminal of the potentiometer in order to enable the normal-operation mode and a second position in which the control line is linked to a node of a divider bridge interposed between the earth terminal and the maximum-voltage terminal of the inverter and comprising two resistors, in order to enable the degraded-operation mode in which the speed of the electric motor is at a minimum value.
According to a first variant, the two resistors of the divider bridge are separate from the potentiometer.
According to a second variant, the potentiometer constitutes one of the two resistors of the divider bridge.
Thus, when the first switch changes from the first position to the second position, the speed of the electric motor is automatically fixed at a chosen value.
According to another characteristic of the invention, the control device comprises a detector associated with the air-conditioning circuit and suitable for causing the first switch to change from the normal-operation mode to the degraded-operation mode as a function of at least one parameter relating to the air-conditioning circuit.
Advantageously, this detector is a temperature sensor associated with the evaporator of the air-conditioning circuit and suitable for detecting an icing-detection temperature.
According to yet another characteristic of the invention, the device comprises at least one detector suitable for closing the second switch as a function of at least one parameter associated with the air-conditioning circuit and/or with an electrical circuit.
Advantageously, the detector is a pressure sensor associated with the air-conditioning circuit and suitable for detecting a high-pressure and/or low-pressure threshold.
According to another characteristic of the invention, the detector detects the stopping of the air conditioning.
According to yet another characteristic of the invention, the potentiometer is driven directly or indirectly via a manual control which can be adjusted by an operator.
In the case of an air-conditioning circuit for a motor vehicle, the potentiometer will be placed on the air-conditioning appliance or behind the control panel. The manual control will be placed on the dashboard of the vehicle and produced, for example, in the form of a slider or of a rotary knob.
Advantageously, the manual control is suitable for achieving continuous control of the speed of the electric motor of the compressor between a minimum speed corresponding to an xe2x80x9call hotxe2x80x9d mode and a maximum speed corresponding to an xe2x80x9call coldxe2x80x9d mode, when the device is in the normal-operation mode.
The potentiometer is preferably linked to the maximum-voltage terminal of the inverter by way of a protective resistor.